The present invention relates to a method and apparatus for processing a linear groove, in order to ensure the safety of passengers upon collision of a vehicle, allowing an air bag portion of a skin made of a resin such as polyvinyl chloride (PVC), polyolefine (TPO), polyurethane (TPU) which forms, for example, an instrument panel of the vehicle to break so as to inflate and deploy an air bag when a destructive force of a predetermined or higher level is applied to the air bag portion upon a collision or the like.
From the viewpoint of design, a linear groove which is to be processed in an air bag portion of a resin skin for a vehicle is requested to be processed not on the side of the front face of the skin but on the side of the rear face. Since the linear groove closely relates to the safety of passengers, it is required that the linear groove should be processed so as to exert a constant breakage resistance which is reproducible. In order to satisfy the request and the requirement, in recent years, means for processing a linear groove from the back-face side of a skin with leaving a predetermined thickness on the front-face side of the skin is generally adopted.
As means for processing a linear groove from the backface side of a skin, conventionally, known are means such as (a) means for processing a linear groove by mechanically cutting away a resin material with a knife-like cutter or the like, and (b) means for processing a linear groove by irradiating a portion to be processed of the skin with a laser beam to locally burn and remove a resin material of the portion, as disclosed in, for example, Japanese Patent Application Laying-Open No. 10-85966.
In the case of the mechanical processing means (a), however, it is technically very difficult to perform the cutting without exposing a linear processing trace to the front-face side of the skin which is to be a design face, even if the cutting is performed from the back-face side of the skin. Therefore, the design face receives large damage. In such a type of processed product, in terms of quality control, it is important to measure the residual thickness on the front-face side of the skin after the processing of the linear groove, and to record and store the data for respective processed products. In the case of the mechanical processing means, the groove width is narrow, and the groove width be comes narrower because opposite faces on both sides of the groove come into close contact with each other due to an elastic force of the resin material immediately after the cutting. For this reason, it is difficult to accurately measure the residual thickness. This is not preferable in terms of quality control.
By contrast, in the case of the laser processing means (b), it is possible to process a predetermined linear groove without applying any damage to the design face (the front face of the skin), but a large output power is required. Thus, the power consumption is high and the processing cost is increased. Particularly, in order to process a wide groove in which the residual thickness that is important in terms of quality control can be accurately measured and easily recorded, it is necessary to use a laser beam generator having an extensive output power, or to cause a laser beam generator having a relatively small output power to trace along a planned process line a plurality of times. This results in a drawback that the processing cost is further increased.
In addition, in order to process a linear groove having a reproducible constant breakage resistance while a predetermined thickness is left on the front-face side of the skin by the laser processing means, it is necessary to delicately control the burned and removed amount of the resin material, i.e., the process depth of the groove in accordance with the variation in thickness of the skin. As means for this purpose, there is no means other than the control of the output power of the laser beam generator. The control in accordance with the variation in thickness of the skin requires sophisticated technology.
Moreover, in the case of the laser processing, the resin material of a skin portion corresponding to a linear groove to be processed is burned and removed. In the process, therefore, soot of an amount corresponding to the burned resin material is generated, and then emitted to the surroundings. If the emitted soot enters the processed groove, the soot causes measured values of the residual thickness to be dispersed. In order to avoid this disadvantage, it is necessary to suppress the generation of soot while an inert gas is used together, and to additionally dispose an apparatus for positively attracting the generated soot and for removing the soot from the processed portion. Thus, there arises a problem in that the cost of installation for the whole processing apparatus is very expensive.
The present invention was developed in view of the circumstances described above. It is an object of the present invention to provide a method and apparatus for processing a linear groove to an air bag portion of a skin for a vehicle in which a linear groove having a reproducible constant breakage resistance with a predetermined residual thickness on a front-face side of the skin can be efficiently processed into an advantageous condition for measuring the residual thickness, while avoiding damage to a design face, and with reduced power consumption and simple control.
The method of processing a linear groove to an air bag portion of a skin for a vehicle according to the invention is a method of processing a linear groove to an air bag portion of a resin skin for a vehicle from a side of a rear face of the skin in a condition where a predetermined thickness is left on a side of a front face thereof, characterized in that, in a condition where the skin is fixedly held so that the front face is closely in contact with a flat face, a position of an oscillating horn of an ultrasonic processing apparatus disposed on the side of the rear face of the skin is adjusted to make a clearance between a front end of the oscillating horn and the flat face coincident with the predetermined residual thickness on the side of the front face of the skin, the ultrasonic processing apparatus and the flat face for fixing the skin are thereafter relatively moved in a direction of a linear groove to be processed, and ultrasonic vibration is sequentially applied to the side of the rear face of the air bag portion of the skin, thereby sequentially fusing and removing a resin for the skin of a portion to which the ultrasonic sonic vibration is applied, to process the linear groove.
The apparatus for processing a linear groove to an air bag portion of a skin for a vehicle according to the invention is an apparatus for processing a linear groove to an air bag portion of a resin skin for a vehicle from a side of a rear face of the skin in a condition where a predetermined thickness is left on a side of a front face thereof, characterized in that the apparatus comprises: a surface table which fixedly holds the skin so that the front face thereof is closely in contact with a flat face; an ultrasonic processing apparatus which is disposed on the side of the rear face of the skin, and which applies ultrasonic vibration to a resin for the skin; a processing position adjusting mechanism which adjusts a position of an oscillating horn of the ultrasonic processing apparatus, to make a clearance between a front end of the oscillating horn and the flat face of the surface table coincident with the predetermined residual thickness on the side of the front face of the skin; and a processing position moving mechanism which relatively moves the ultrasonic processing apparatus and the surface table in a direction of a linear groove to be processed.
According to the invention with the above-mentioned configuration requirements, as means for processing a linear groove from a back-face side of the resin skin, ultrasonic vibration by the ultrasonic processing apparatus is utilized. The position of the front end of the oscillating horn is adjusted in the thickness direction of the skin, so that the clearance between the horn end and the flat face with which the front face of the skin is closely in contact coincides with the predetermined thickness to be left on the front-face side of the skin. In this condition, the ultrasonic processing apparatus and the flat face for fixing the skin are relatively moved (traced) once in the direction of a linear groove to be processed, i.e., along a planned process line. Simply by the above, the resin for the skin in the traced portion can be fused and removed, so as to process a wide linear groove having a predetermined depth. The fused resin caused by the ultrasonic processing is removed to sides of the groove, and hardened. Thus, any foreign material cannot enter the groove. Therefore, a linear processing trace which appears in the case of the mechanical processing is not exposed to the front-face side, so that damages to the design face can be avoided. In addition, the processing position corresponding to the variation in thickness of the skin can be easily adjusted by a simple mechanical control. Consequently, a linear groove having a predetermined residual thickness on the front-face side of the skin and having a reproducible constant breakage resistance can be efficiently processed. Moreover, the fused resin caused by the ultrasonic processing is removed to the sides of the groove and hardened, so that the fused resin will not enter the groove. Unlike the laser processing, therefore, it is entirely unnecessary to provide means for suppressing the generation of soot due to the groove processing, and means for attracting the generated soot and removing the soot to a place distant from the processed portion. While the processing cost can be remarkably reduced by the reduction of the installation cost for the whole of the apparatus and the reduction of the power consumption, the residual thickness on the front-face side of the skin after the groove processing can be easily and accurately measured from the back-face side. As a result, the invention attains an effect that the quality control in which data for respective processed products are recorded and stored can be appropriately and accurately performed.
In the method and apparatus for processing a linear groove to an air bag portion of a skin for a vehicle as described above, a configuration may be employed in which cooling air is blown to a skin portion immediately after the linear groove is processed by ultrasonic vibration, to cool and harden the fused resin. According to the configuration, the processing efficiency is improved, and the resin portion which is fused by the ultrasonic vibration and removed to the sides of the groove can be immediately hardened. Therefore, a foreign material which causes an error in measurement of the residual thickness is surely prevented from entering the processed groove, whereby the accuracy of the measurement of the residual thickness can be enhanced and the reliability of the quality control can be further increased.
In the method and apparatus for processing a linear groove to an air bag portion of a skin for a vehicle, a configuration may be employed in which a portion to be processed of the skin immediately before the application of the ultrasonic vibration is previously heated. According to this configuration, the portion to be processed is previously softened, and stress in the ultrasonic processing is dispersed, whereby damages to the design face on the front-face side can be further surely avoided. Moreover, the processing for a wider groove can be surely performed.
Alternatively, in the method and apparatus for processing a linear groove to an air bag portion of a skin for a vehicle, a configuration may be employed in which a portion to be processed of the skin immediately before the application of the ultrasonic vibration is previously heated, and cooling air is blown to the skin portion immediately after the processing of the linear groove, so as to cool and harden the fused resin. Therefore, the processing efficiency is improved, damages to the design face are avoided, and at the same time foreign materials are prevented from entering the groove, so that the reliability of the quality control can be further improved.